There has been a great deal of interest in developing better and more efficient methods for storing energy for applications such as radio communication, satellites, portable computers, and electric vehicles to name but a few. Accordingly, there has been recent concerted efforts to develop high energy, cost effective batteries and/or electrochemical capacitors having improved performance characteristics.
Rechargeable or secondary cells are more desirable than primary (non-rechargeable) cells since the associated chemical reactions which take place at the positive and negative electrodes of the battery are reversible. Electrodes for secondary cells are capable of being regenerated (i.e., recharged) many times by the application of an electrical charge thereto. Numerous advanced electrode systems have been developed for storing electrical charge. Concurrently, much effort has been dedicated to the development of electrolytes capable of enhancing the capabilities of electrochemical cells.
Heretofore electrolytes have been either liquid electrolytes as found in conventional wet cell batteries or solid films as are available in newer, more advanced battery systems. Each of these systems have advantages, though they have inherent limitations which make them unsuitable for particular applications. Liquid electrolytes, while demonstrating acceptable ionic conductivity, tend to leak out of the cells in which they are sealed. While better manufacturing techniques have lessened the occurrence of leakage, cells still do leak potentially dangerous liquid electrolytes from time to time. Moreover, any leakage in the cell lessens the amount of electrolyte available to the cell, thus reducing the effectiveness of the cell.
Conversely, solid electrolytes are free from problems of leakage. However, they have vastly inferior properties as compared to liquid electrolytes. For example, conventional solid electrolytes have ionic conductivities in the range of 10.sup.-5 S/cm whereas acceptable ionic conductivity is typically greater than about 10.sup.-3 S/cm. Good ionic conductivity is necessary to ensure a battery system capable of delivering usable amounts of power for a given application. Good conductivity is necessary for the high rate operation demanded by, for example, cellular telephones and satellites. Accordingly, solid electrolytes are not yet adequate for many high performance battery systems.
One solution which has been proposed relates to the use of gel electrolytes for electrochemical systems. These types of electrolytes have not been entirely successful as they tend to dissolve in the electrolyte solvent, thus losing mechanical integrity. As mechanical integrity is lost, the conductivity of the solution is compromised and hence performance of the electrochemical cell is degraded. Moreover, as the gel loses mechanical integrity, it becomes a liquid, and is once again subjected to the problem of leakage.
Accordingly, there exists a need for a new electrolyte system which combines the mechanical stability and freedom from leakage offered by solid electrolytes, with a high ionic conductivity characteristic of aqueous, liquid electrolytes.